Back in coach where we sit on either LAX-LHR or PHX-LHR we have always been offered water (or orange juice) almost constantly. We've had crew members going up and down the aisles with water all through the flt. and offering it before taking off as well. I always take a bottle of water anyway, but never felt like BA was rationing the stuff. If I did I'd go to the galley and get some. BA has a lot of faults but so far water rationing hasn't been one of them as far as I've noticed :-)